This application is a 371 of PCT/FR00/00245 filed May 4, 2000.
The present invention relates to a segregation reducing agent prepared by alkalifying a curdlan-producing fermentation broth per se or a curdlan powder in solution with alkaline material, and also relates to hydraulic compositions, concrete and mortar, comprising the segregation reducing agent. This segregation reducing agent can provide a great resistance to segregation for hydraulic compositions even at its small amount as well as guarantee the strength, filling ability and fluidity.
As main concrete materials, there are specifically enumerated cement, water, fine aggregate and coarse aggregate. However, recent increasingly intensive interest in the high strength and durability of concrete as well as in the economizing of construction with concrete has directed active research toward the development of admixtures capable of providing a variety of functions to concrete. Such admixtures may be representatively exemplified by an AE agent (air entrainment agent), a water-reducing agent and an AE water-reducing agent. Offering a variety of functions, including the improvement of concrete workability, the augmentation of resistance to freezing and thawing, the reduction of the cement amount to be used by virtue of water reducing effect, and the strengthening of concrete strength, the admixtures are recognized as the fifth ingredient for concrete. Generally, the water-reducing agent can bring about a reduction of water by 10 to 30%. However, overuse of the water-reducing agent makes worse the physical properties of concrete, as in the increase of air entrapment and the segregation of the material ingredients.
With he aim of repressing these side effects, polysaccharides have been added as an admixture for concrete. They function to enhance the viscosity of concrete, so as to suppress the segregation of material ingredients and increase the fluidity of concrete.
It is known that a broad spectrum of microbes is able to produce polysaccharides. Polysaccharides that microbes extracelluarly secrete are quite different in terms of molecular weight, kinds of constitutive sugar units, the order, type and position of the linkages between sugar units, and the existence of branches, depending on strains and culture methods. They also exhibit different gelability, emulsion stability, surface tension controllability, water absorptivity, tackifying property, lubricating ability, and. film forming property from one another. Numerous applications of polysaccharides, which are mainly produced from microorganisms, exist in the food, cosmetic, petroleum and paper industries. For instance, they are used as stabilizers, emulsifiers, and thickeners in the food industry. Also, they are useful for excavating or crude petroleum-recovering processes in the petrochemical industry. In addition, polysaccharides have recently been applied for the drag reduction for ships and to make high value-added bio-medicines as well as being newly developed as admixtures for construction.
Curdlan, which Agrobacterum spp. and Alcaligenes faecalls secrete from these cells into an extracellular space, is a water-insoluble, neutral polysaccharide which consists of glucose units bonded to each other through beta-1,3-glycosidic linkage. This homopolymer shows a characteristic physicochemical property of irreversibly forming gel when being heated, so that it is added as a thickener for foods. Thus, the polysaccharide finds numerous applications, including jelly foods, food fibers, film and immobilized carriers (Paul et al., Biotechnol. Adv., 4:245-259, 1986). Particularly, there are disclosed many patents pertaining to use of curdlan as segregation reducing agents for concrete materials.
For example, Korean Pat. No. 144454 (1998), yielded to Daisei Construction. Co. Ltd., Japan and Takeda Chemical Industries, Ltd., Japan, discloses that a powder of beta-1,3-glucan is added to increase the viscosity of a hydraulic composition comprising a binder to suppress the segregation among the materials of the composition and enhance the fluidity of the composition. However, the quantity of curdlan used in the reference patent amounts to from at least 1.36 to 2.96 kg per unit volume (m3) of concrete, giving rise to a large increase in the cost of concrete.
Takeda Industries Ltd., Japan, also discloses in U.S. Pat. No. 5,376,173 a segregation reducing agent which is obtained by adding a highly viscous polysaccharide such as xanthan or methylated cellulose to a culture of a microorganism capable of producing curdlan and drying the mixture to give a powder. In this segregation reducing agent, the employed polysaccharides, that is, a mixture of curdlan and another polysaccharide amounts to as much as 1.6 kg/m3 of concrete, suffering from a disadvantage of increasing the production cost of concrete.
U.S. Pat. No. 5,573,589 describes chemical modification of curdlan in which curdlan is treated with sulfate (SO3xe2x88x92) to produce curdlan sulfate which is then used as an admixture for concrete. However, the curdlan used for the preparation of the curdlan sulfate amounts to from as much as 1.75 to 3.15 kg/m3 of concrete, depending on the uses of the modified curdlan.
In the prior arts described above, a powdering process is required for curdlan or its derivatives to be used as a segregation reducing agent for concrete, giving rise to an increase in the production cost, there is needed a collateral cost for the derivatives or auxiliary additives serving to enhance the viscosity of concrete, and the powder should be added at an amount of as much as 1 kg per lube (m3) of concrete in order to show an effect as a segregation reducing agent.
Thus, there remains a need for developing a segregation reducing agent which is simple in its preparation and has a great effect even at a small amount, thereby reducing the production cost.
Leading to the present invention, the intensive and thorough research on segregation reducing agents for hydraulic compositions, repeated by the present invention aiming to use curdlan with a great economical advantage, resulted in the finding that the alkalifying of curdlan powder or a curdlan-producing fermentation broth gives a curdlan solution of high viscosity which brings about a maximal effect in the resistance to segregation with its small amounts and that use of the curdlan-producing fermentation broth itself can eliminate the cost for powdering equipments and processes.
It is an object of the present invention to overcome the above problems encountered in prior arts and to provide a segregation reducing agent for a hydraulic composition, which brings about a great improvement in resistance to segregation with an economical advantage.
It is another object of the present invention to provide a hydraulic composition containing such a segregation reducing agent.
Based on the present invention, the above objects could be accomplished by a provision of a segregation reducing agent for hydraulic compositions, comprising curdlan and an alkaline material.
Also, in accordance with the present invention, there is provided a hydraulic composition comprising such a segregation reducing agent.
In the present invention, curdlan is obtained from a fermentation broth which contains sugar or raw sugar as a carbon source and ammonium chloride as a nitrogen source, in combination with other inorganic salts. As microorganisms grow in the medium, curdlan is secreted from the cells. Preferably, although not necessarily, the curdlan may be purified for use.
Purification of raw curdlan is carried out as follows. A fermentation broth highly rich in curdlan is controlled in neutral pH during growth and production phase. Since curdlan is not dissolved in a neutral solution, curdlan exists as a water-insoluble form. The fermentation broth is alkalified to solubilize the curdlan which is then able to be separated from the cells by centrifugation or filtration. After removal of the cells, the resulting solution is brought into contact with an aqueous organic solution or neutralized to cause the precipitation of curdlan. After being collected by centrifugation, the precipitates are dried to afford purified curdlan powder.
The present invention provides a segregation reducing agent comprising a curdlan-producing fermentation broth itself or a curdlan powder in combination with alkaline material. This segregation reducing agent is prepared and mixed to a hydraulic composition for use as follows.
First, a curdlan-producing fermentation broth itself is used as a segregation reducing agent. One or more of the alkaline solution group consisting of NaOH, KOH, NH4OH, and Ca(OH)2 is added into the fermentation broth, giving an alkaline curdlan solution with pH 10 or higher. This alkaline curdlan solution can be used in its integrity as a segregation reducing agent for hydraulic compositions, such as concrete, mortar and the like. By way of example, NaOH is added at an amount of 2.0 to 20.0 g per liter of the fermentation broth. A hydraulic composition typically comprises cement, water, sand and pebbles and may be added with admixtures such as an AE agent, an AE water-reducing agent, a water reducing agent, etc. Examples of these agents include naphthalene type agents, melamine type agents, carboxylic acid type agents and lignin type agents.
Alternatively, the alkaline curdlan solution is obtained from curdlan powder. The curdlan powder may be prepared by drying the curdlan-producing culture and atomizing the dried residue or by the above described purification process from the culture.
The curdlan of the segregation reducing agent can guarantee a segregation reducing effect at an amount of as low as 0.48 kg per 1 lube of hydraulic composition such as concrete. More amounts than this secure resistance against the segregation of materials as a matter of course and further, reinforce the compression strength of the concrete. A little less amount of the curdlan allows somewhat segregation of the materials, but shows similar compression strength or slump properties to those at the suggested amount.
Therefore, the segregation reducing agent prepared by mixing curdlan with an alkaline material according to the present Invention can bring about a maximal effect on the resistance to segregation even at a small amount, unlike conventional segregation reducing agents.
There is a need to examine the segregation reducing effect of the segregation reducing agent on a hydraulic composition such as concrete. In this regard, a hydraulic concrete composition is prepared, followed by measuring the segregation reducing agent for segregation reduction and fluidity improvement. To prepare one lube (m3) of the concrete composition, 150-200 kg of water, 300-500 kg of a cement-containing binder, 350-900 kg of sand, and 600-1,000 g of pebbles are mixed in combination with 5-15 kg of a water-reducing agent and 5-50 kg of the segregation reducing agent consisting of curdlan and alkaline material. The curdlan is preferably used at an amount of 0.15-1.5 kg per lube of concrete. To make a hydraulic concrete composition, cement, sand and pebbles are mixed for 1 min in the absence of water in a stirrer with a diameter of 75 cm, and then stirred for 3 min at a stirring speed of 30 rpm, along with water, a water-reducing agent and the segregation reducing agent. The fluidity and strength of the composition are measured.
The segregation reducing agent of the present invention can be also used as an admixture for a mortar. To prove the segregation reducing agent worthy of an admixture, a hydraulic mortar composition 1s prepared, followed by evaluating the segregation reducing agent for segregation reduction and fluidity improvement. To prepare one lube (m3) of a mortar concrete composition, 500-650 kg of water, 700-850 kg of cement, and 1,600-1,900 kg of sand are mixed in combination with 100-200 g of a naphthalene-based water-reducing agent and 0.2-1 kg of the segregation reducing agent. Cement and sand are mixed for 1 min in the absence of water in a stirrer with a diameter of 75 cm, and then stirred for 3 min at a stirring speed of 30 rpm, along with water, a water-reducing agent and the segregation reducing agent to give a hydraulic mortar composition and a measurement is made of the fluidity and strength of the composition.
Practical and presently preferred embodiments of the present invention are illustrative as shown in the following examples.
However, it will be appreciated that those skilled in the art on consideration of this disclosure, may make modifications and improvements within the spirit and scope of the present invention.